Add Proxy-Authorization header token at settings file

[riqueps]

Is your feature request related to a problem? Please describe.
With --header flag on epinioCLI is capable to access epinioApi protect by GCP IAP solution.
But is kinda boring need to add the --header on each command after the login.

Eg:

• epinio login -u XXX -p YYY https://epinio.domain.com --header "Proxy-Authorization: Bearer ID_TOKEN"
• epinio app list --header "Proxy-Authorization: Bearer ID_TOKEN"
• epinio service create... --header "Proxy-Authorization: Bearer ID_TOKEN"
  and so on.

Describe the solution you'd like
Would be nice, once we pass the --header flag during the login epinioCli automatically add the Proxy-Authorization: Bearer token at epinio settings.yaml file and use it for further requests.
Meaning, as a epinio user, I just need to use the --header just on the login and when the TOKEN expired I need to generate a new token and login again.

Eg:

• epinio login -u XXX -p YYY https://epinio.domain.com --header "Proxy-Authorization: Bearer ID_TOKEN"
• epinio app list
• epinio service create...
  and so on